EAF, Transferability to Operation and Improving Prospects

Environment assisted fatigue (EAF) research in simulated reactor coolant waters has shown variable reductions in fatigue lives of laboratory specimens. Unless otherwise shown, the results are assumed transferable to the pressure boundaries of primary coolant circuits. By experiments and regression analysis determined environmental penalty factors have been adopted as means to adjust the allowable numbers of fatigue transients in reactor components. These Fen factors play a central role in transfer of EAF lab data to fatigue management and risk informed inspection at the plant. This paper reports lessons learned in experimental and analytical research of EAF aiming to understand and reliably measure Fen factors for improved transferability to the codified fatigue assessment of stainless reactor components. We have earlier reported inability to repeat the Fen factors proposed for the conservative high temperature & low-rate edge, when applying direct strain control in PWR water. This issue and ongoing research aiming to develop improved Fen models will be addressed. In addition, a thermodynamic point of view is introduced and discussed. The thermodynamic model fits poorly to the lowest Fen factors for low temperatures and/or high strain rates, which is probably also an area not well supported by experimental data but may still be relevant in PWR operation. Challenges in determining Fen factors, their transferability to plant operation and possibilities for improvements will be discussed.